The present invention relates to a method of and to an apparatus for making a stream from particles of the tobacco processing industry, particularly from particles of natural, reconstituted or substitute tobacco and mixtures thereof, or from particles which are used in the fillers of filter rods to produce mouthpieces for cigarettes, cigars, cigarillos and like rod-shaped smokers' products.
For the sake of simplicity, the following description will deal with the making of cigarettes. However, it is to be understood that the stream which is formed and processed in accordance with the present invention can be made from particles or fragments other than those constituting the smokable part of a plain or filter cigarette, cigarillo, cigar or cheroot.
It is well known to make a cigarette rod by showering or otherwise delivering fragments of tobacco leaves, fragments of reconstituted tobacco sheets and/or fragments of substitute tobacco onto a circulating air-permeable endless belt conveyor which travels along a suction chamber to attract a growing tobacco stream and to advance the stream past a trimmer which removes the surplus before the resulting trimmed or equalized stream is draped into a web of cigarette paper or the like and is subdivided into cigarettes of unit length or multiple unit length. It is also known to monitor the density of the trimmed stream, of the filler in the cigarette rod and/or of the fillers in discrete cigarettes, and to adjust the trimming device so as to ensure that the density of the tobacco filler will match or closely approximate a desired value. The density measurement is or can be carried out in such a way that the monitoring device ascertains the densities of successive increments or unit lengths of the stream, i.e., the densities of successive slabs of the stream extending at right angles to the direction of advancement of the stream along its path. Another known monitoring device comprises an array of detectors which are disposed in a row extending at right angles to the direction of travel of the stream and serve to generate signals denoting the densities of adjacent layers of the stream. The detectors generate signals in accordance with the intensity of radiation (particularly beta rays) which is capable of penetrating through the stream. The intensity of radiation which has penetrated through the stream is proportional to the density of the corresponding layers of the stream. The trimmer is movable relative to the path of the tobacco stream, i.e., nearer to or further away from the surface of the conveyor which attracts and transports the stream past the trimming station.
A method and apparatus of the above outlined character are disclosed in the commonly owned copending patent application Ser. No. 572,563 filed Jan. 18, 1984 now U.S. Pat. No. 4,785,830. In the apparatus of this copending application, fibrous material which is to form the stream is loosened in a distributor (also called hopper) and is showered into or otherwise delivered to a stream building station to be attracted by a driven air-permeable endless belt conveyor whereon the particles form a growing stream. The fully grown stream is advanced to the trimmer which removes the surplus, and the resulting trimmed stream is densified, draped to form a cigarette rod and conveyed through a cutoff to yield a succession of cigarettes of unit length or multiple unit length. The rod is monitored to ascertain the density of its filler, and the signals are used to adjust (when necessary) the position of the trimmer with reference to the conveyor.
The apparatus which is disclosed in the patent application Ser. No. 572,563, now U.S. Pat. No. 4,785,838, includes position-sensitive detectors which are designed to determine the density of several layers of the stream. Signals which are generated by the detectors furnish information concerning the distribution of density across the stream. Such signals are used to influence the formation of the stream in order to ensure the formation of a stream having a desired or optimum density profile.
As mentioned above, the density of the filler in the cigarette rod is normally determined with a beta ray detector. However U.S. Pat. No. 3,056,026 to Bigelow discloses a modified detector which operates with a source of X-rays and with an ionization chamber serving to receive radiation which has penetrated across the tobacco stream. Each of these conventional monitoring devices is capable of generating signals which denote the density profile of the monitored stream.
A drawback of conventional apparatus is that they do not embody any means which could be used to ascertain the filling power of tobacco and/or to influence the hardness of the cigarette rod and/or the hardness of individual smokers' articles. Moreover, heretofore known apparatus do not embody any suitable practical means for optimizing the quantity of surplus tobacco in the stream which advances toward the trimming station.